1. Field of the Invention
The present invention relates to a separable fastening component being widely used in the field of clothing. More specifically, the present invention relates to a thin, flexible separable fastening component having a sufficient engaging force and an agreeable touch, which is suitably used for disposable diapers and like applications that directly or indirectly contact the human skin.
2. Description of the Prior Art
Known separable fasteners include what is known as hook-type separable fastener comprising a female fastening component comprising a base and a multiplicity of loops provided thereon (hereinafter sometimes referred to as "female surface") and a male fastening component comprising a base and, provided thereon, a multiplicity of hook-shaped fastening elements formed from thick monofilaments (see, for example, Japanese Patent Publication No. 522/1960) and a what is known as mushroom-type separable fastener comprising a male fastening component comprising a base and, provided thereon, a multiplicity of mushroom-shaped fastening elements formed by fusing and swelling the ends of thick thermoplastic resin monofilaments with a hot plate or like means and the above female separable fastening component (see, for example Japanese Patent Publication No. 22501/1978 and Japanese Patent Application Laid-open No. 38734/1974). With both of these separable fasteners, the hook-shaped fastening elements or mushroom-shaped fastening elements of the male separable fastener (hereinafter sometimes referred to as "male surface") engage with the loops of the female separable fastener, to produce an engaging force. Accordingly, these fasteners are of male-female type. On the other hand, also known is a male-male type (homo-type) which uses a combination of the same two male fastening components, comprising fastening elements comprising a multiplicity of bundles which comprises a plurality of monofilaments with their tips being fused together (see Japanese Patent Publication No. 12340/1970 and Japanese Utility Model Application Laid-open No. 123106/1992).
However, the above hook-type male separable fastening component should have a limited height of the hooks, since the hooks are prepared by inserting the tip of a clipper into loops constituting precursors for the hooks and hence the height of the loops, i.e. that of the hooks formed therefrom, is so restricted as to be able to introduce the clipper. Consequently, attempts to make thin the hook-type fastening component have only succeeded in obtaining a minimum thickness including the base of about 1.3 mm. This type male separable fastening component, utilizing thick monofilaments for hooks, has another disadvantage of giving a coarse touch.
On the other hand, while known mushroom-type male separable fastening components comprising a multiplicity of mushroom-shaped elements formed from single monofilaments also use, generally, thick monofilaments to obtain an engaging force of a level suited for practical purposes, development of a thinner, more flexible type is desired for use in disposable diapers and like uses. To make thin a mushroom-type male separable fastening component may be possible to some extent, even with thick monofilaments, by increasing the amount fused of the tips to decrease the height of the fastening elements. However, the thickness (thinness) of the fastening component is still limited due to the following points. That is, making thin to a level below a limit requires increasing the amount fused of thick monofilaments having a large heat capacity, thereby prolonging the heating time, and also requires placing a heat source such as high-temperature hot plate near the base surface. As a result, the base tends to deform so that the entire separable fastening component will curl or wave.
Besides, mushroom-type fastening elements comprising single monofilaments lose their engaging force just when their swollen heads are torn off during use. This type fastening element further has the following drawback. Use of polypropylene or polyethylene monofilaments with low melting point assures formation of swollen heads with sharp-angled bottom, i.e. true mushroom shape, which hardly permits the loops having engaged therewith to become disengaged and thus produces high engaging force. However, the swollen heads tend to be torn off when the counterpart female component is peeled off, thus being of poor durability. Thermoplastic monofilaments other than the above polyolefins, such as nylon and polyester, are readily dyeable and have high melting point so that ironing can cause no fear of fusing. In particular, nylon has the advantage of exhibiting soft and agreeable touch under the usual conditions of temperature and humidity. However, use of nylon or polyester monofilaments causes the resulting swollen heads to have spherical shape, so-called "match-shape", thereby being incapable of providing high engaging force. See, for example, Journal of the Textile Institute, Vol. 79, No. 4, pages 672-675 (1988).
As described so far, conventional male separable fastening components, both hook-type and mushroom-type, use thick monofilaments for their fastening elements and are hence difficult to decrease the thickness and have coarse hand lacking flexibility. Use of fine monofilaments can produce no good engaging force for practical purposes, while they should give small thickness and good flexibility though.
Examples of the afore-mentioned separable fastening components having fastening elements each of which comprises a plurality of monofilaments whose ends are fused together are as follows. Japanese Patent Publication No. 12340/1970 discloses a separable fastening component comprising a base and, provided thereon, a multiplicity of "rail-shaped" (i.e. resembling a bar like a railroad rail having a T-shaped cross-section) fastening elements comprising a line of bundles of raised filaments whose ends are successively fused together. However, this type separable fastening component, having rail-shaped fastening elements, engages with its counterpart by insertion of the rail-shaped fastening elements into each other. Thus, this constitutes so-called a "homo-type" separable fastener and is not intended to engage with a female fastening component. With this type, the base is difficult to bend so that the entire fastening component has also insufficient flexibility. Japanese Utility Model Application Laid-open No. 123106/1992 discloses a fastening component comprising a base and mushroom-type fastening elements each of which comprises a plurality of monofilaments raised from different points on the base surface, the heads of the monofilaments being integrally fused together. However, this type fastening component is, engaging with its counterpart by insertion of the fused head parts into each other, also used for homo-type. This type, with the monofilaments constituting the fastening elements having a large fineness of 250 to 1,300 deniers, is not suited for engagement with a female fastening component. This type has a coarse touch and, further, a large thickness of 2 to 5 mm of the base alone, thereby being not flexible. In any case, the above-described separable fastening components are not suitable for direct engagement with a thin, inexpensive female surface, such as loop- or pile-stuff being used for disposable diapers or the like.